Carrier telegraph terminal circuit



Feb. 26, 1946. J. BRUNDAGE v 2,395,451

CARRIER IETJEGIKTAPH TERMINAL CIRCUIT.

Filed April 18. 1944 Race! why a r Ciro uit IN V EN TOR.

JOHN HOLT BRUNDAGE A TTORNE K Patented Feb. 26, 1946 UNITED STATES ?ATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to improvements in telegraph signalling circuits, and it is more particularly directed to differential telegraph loop circuits of the character utilized in conjunction with carrier current systems. 7

Carrier telegraphy is employed for the purpose of greatly increasing the message carrying capacity of a telegraph circuit by permitting the simultaneous transmission of a plurality of signals on a single line. Two systems of carrier telegraphy are in common use; namely, the low frequency system utilizing a frequency range from about 400 to 2,400 cycles or higher, depending on the number of channels, and the high frequency system-utilizing a frequency range from about 3,000 to about 11,000 cycles.

A basic unit of a carrier system is composed of an oscillator, operating in the carrier frequency range and fed to the outgoing line, said oscillator being modulated by the D. C. telegraph signals originating at a loop terminal, and a receiver connected to the incoming line, which serves to demodulate the received carrier telegraph signals to its initial D. C. form thereby activating a neutral sounder in the loop terminal. A plurality of such units may be bridged across identical outgoing and incoming lines without mutual interference as long as the carrier oscillators have distinctly separated frequencies and the receivers are resonant to desired oscillator frequencies.

In differential duplex loop circuits employed in association with carrier telegraph apparatus, the circuits are usually opened and closed by a telegraph key in series with a loop circuit when signals are conveyed from the loop to the outgoing carrier line. They normally have the polarity of the loop line as impressed thereon by a battery at the distant end of the loop and when signals are being received from an incoming carrier line, the polarity of the'loop is reversed by the receiving relay. The transmission of signals from the incoming carrier line to'the subscribers loop is accomplished by applying polar signals to the apex of the loop circuit. These polar signals when working in opposition to the battery at the distant end of the loop results in the open and close operation of the neutral sounder functioning in the loop circuit.

My invention is applicable to those telegraphic systems wherein a singl alternating current,

used for the transmission of a single series of messages. It is also applicable to .those systems wherein several alternating currents, alone or in combination with a direct current, areused for the simultaneous transmission of a plurality of messages.

It is one of the main objects of my invention to provide improved apparatus in loop circuits for enabling the loop subscribers to control the transmission of carrier signals to the main line from his loop. I

An additional object of my invention is to provide positive means for transmitting a break signal from a loop circuit to a distant operator over a carrier current telegraph system. i

\A further object of my invention is to provide improved circuits for transmitting a positive break signal from the loop to the main line requiring only two relays for the performance of this operation as compared to the three relays conventionally used heretofore for this purpose.

To the accomplishment of the foregoing general objects and other more specific objects which will hereinafter appear, my invention resides in the method and apparatus elements and their relation one to the other as are hereinafter described in greater detail in the following specification, the specification being accompanied by a drawing in which the single figure illustrates a schematic circuit diagram of my invention for half-duplexing an alternating current or carrier telegraph system. l

The circuit disclosed in the drawing is the carrier terminal arrangement for either a local or a distant subscriber.

Since both subscribers have identical arrangements, it has not been necessary to illustrate both ends of the duplex system.

Referring now to the drawing, the basic components of the circuit consist of a subscribers loop circuit It), a transmitting relay H, a receiving relay I2, a carrier receiving circuit l3, a carrier frequency generator l4, and a carrier modulator l5. The transmitting relay I I is of a polarized type, having a pair of windings A and B and an armature in cooperation with marking and spacing contacts. The relay characteristics are such thatwhen a current flows in one winding in one direction and a current of equal intensity flows in the other winding but in an opposite direction, the resultant magnetic fields cancel, and the armature remains in a neutral position. If, however, there is a disparity in the currentintensities in the two windings, or if thecurrent flowing in both windalone or in combination with direct current, is ings are in the same direction, the armature will shift to one of the contacts depending on the overall polarity of the field.

Connected to terminal M of the polar relay II is a loop circuit I comprising a telegraph key I6, having a shorting switch shunted thereon, and a telegraph sounder I! in series connection with key I6. Although for the purposes of simplicity, the loop circuit is described as having a key and a sounder, in practice a teletypewriteror similar communication devices may be used in the circuit.

The loop circuit is energized by a battery I8 connected between one end of the sounder I1 and ground. An artificial line I9 is connected between terminal 23 of the polar relay I I and ground. The artificial line I9 is in the form of a resistance-capacitance network which is adjusted to match the impedance characteristics of the loop line.

Connected between the armature of polar relay I I and ground is a modulator I which functions as a control device for a carrier frequency generator I4. The output of generator I4 is fed to the outgoing line. The generator I4 has an operating frequency within the carrier range, and is of conventional design, being of the tuning fork, vacuum tube oscillator, or high frequency alternator type. The modulator I5, preferably in the form of an electronic switch, is triggered by the voltages applied through the armature of relay II, and in effect functions as a key in thecircuit of generator I4.

A battery is provided, having its negative terminal connected to the spacing contact of polar relay I I, and its positive. terminal to ground. An identical battery 2I has its positive terminal connected to the marking contact of relay I I and its negative terminal to ground. In operation, when the relay II is on mark, the positive polarity applied to the modulator I5 causes the generator 54 to transmita mark signal on the outgoing line, whereas when the armature is on, space the negative polarity applied to the modulator effects a break or av space in the. carrier transmission.

The incoming line is terminated in, a receiver I 3 of conventional design including peaked filter means for selecting a desired incoming frequency, a detector for converting the carrier signals to its original direct current form and suitable amplifier means thereafter. The output yielded by receiver I3 isimposed upon the. receiving relay I2 which is of a neutral type, having an armature in cooperation with the marking andspacing contacts. When no current flows through relay I2 a spring serves to maintain the armature on the spacing contact.

As is the common practice in telegraph syste'm's, when both local and distant subscribers have their circuits idle, an uninterrupted carrier current is maintained on the outgoing and incoming lines. Accordingly, the incoming carrier current is selected, rectified and amplified by receiver I3, thereby operating relay I2 and causing its armature to make connection with the marking contact. A battery 22 having its negative terminal attached to the marking contact of relay I2 and itsnegative terminal toground is brought into the circuit when relay I2 marks. Likewise, in the idle condition, the local subscriber closes the switch on key I 6, thus complete ing the loop circuit and applying the potential of battery I8 in series with battery 22 through the A winding of transmitting relay II. While the current flow from batteries 22 and I8 are in series connection in respect to winding A of relay II, they oppose with respectto winding B. When a negative polarity is applied to the apex 25 oi,

relay II and a current flows in the A winding, the armature is caused to shift to mark whereas if the current flows in the B winding the arma ture moves to space. Conversely, when a positive polarity is applied to the apex 25 and a current flows in A, the armature spaces whereas when a current flows in B the armature marks. Hence, in this instance the armature of the relay II is made to close on the marking contact and the positive polarity of battery 2| is applied to the modulator I5, causing the generator I4 to transmit a continuous carrier current on the outgoing line.

When the local subscriber wishes to transmit a break over the outgoing line in order to gain control of the circuit for the purpose of transmitting a telegraph message, he opens the switch on telegraph key I5, thereby opening the loop' circuit and'disconnecting battery I8 from relay II. As a result, the A winding circuit of relay I I is open and the negative polarity from battery 22 is applied to the B winding of the relay, causing the armature to shift to the space contact thereof thereby connecting the negative terminal of battery 2a to modulator I5 with a resultant break in the outgoing carrier. Thus, it may be seen that as the loop I0 is opened and closed the transmitting relay I I shifts from space to mark. After the transmission of the'break, the local operator then proceeds to work the telegraph key in accordance with themessage to. be

transmitted. The D. C. signals originating at the loop operate the transmitting relay II in the manner above described, and, by means of modulator I5 and generator I4, are converted into corresponding A. C. carrier signals.

It is to be noted that the distant subscriber has no control over the local subscriber once the. break has been made by the latter and transmitting relay II is positioned on space. With transmitting relay I I on space, if the distant subscriber breaks and relay I2 goes from imark" to space, the polarity applied to apex: 25 of transmitting relay II remains unchanged since when relay I2 is on space the negative end of battery 20 is applied and when .relay I2 is on mark the negative end of battery 22 is applied. Consequently in both conditions transmitting relay II is unaffected.

The incoming signals are unable in any case to affect the outgoing carrier by altering the position of transmitting relay II as determined by the loop It]. When the loop I0 is closed and relay I2 is on mark, battery 22 functions in series connection with battery I8 to actuate the A winding of relay II and shift the armature to mark. When the loop is closed and the incoming signal breaks causing relay I2 to shift t space, the positive terminal of battery 21 i applied to the apex 25 of transmitting relay II where it opposes battery I8 in winding A and parallels said battery in winding B thereby caus 7 ing transmitting relay II to remain on mark. Accordingly it may be seen that irrespective of whether relay I2 is on mark or space" as dee termined by the incoming signals, transmitting relay H is unaffected when the loop isclosed.

When the local subscriber wishes to receive, he closes the switch on key I6. The incoming signals operate relay I2 in accordance with the message, thus applying a negative potential to the apex 25 of transmitting relay II from battery 22 when a mark is made by the distant sender and a positive potential from battery 2I to'the apex '25 of transmitting relay II when relay l2 spaces. As a result, batterie 22 and 2| are alternately in current coincidence and opposition with battery l8 in respect to sounder l1, and the sounder is thereby operated.

It is believed that the construction and operation of my improved telegraph signalling circuit, as well as the many advantages thereof, will be apparent from the foregoing detailed description. The invention is of particular value in connection with carrier telegraph systems and i illustrated as applied to such systems for that reason, and also by way of exemplification of the invention, but not in limitation thereof. In addition to its possible application to an alternating current telegraph system, or a carrier telegraph system as indicated, the apparatus shown may also be applied to any metallic or grounded duplex telegraph system using a polarized difierential loop circuit for half duplex operation.

It will, therefore, be apparent that while I have shown and described my invention in a preferred improvement, many changes and modifications may be made without departing from the spirit of the invention as sought to be defined in the following claim.

Iclaim:

The combination in a telegraph system, comprising a carrier receiving channel, a\carrier transmitting channel, a direct current telegraph loop, a balancing circuit for said loop, a'polarized relay having windings in said balancing circuit and said loop, a modulator associated with said transmitting channel and controlled by said polarized relay, a receiving relay associated with said carrier receiving channel and having its armature connected to the apex of said relay windings, a source of current connected to one contact of said receiving relay, a second source of current, a circuit from the armature of said polarized relay to the second contact of said receiving relay to connect said second source of current of the same polarity to the second contact of said receiving relay thereby to prevent the operation of said polarized relay when 'actuated by received signals during period when said loop is open.

JOHN HOLT BRUNDAGE. 

